Telecommunication networks, particularly for radio-mobile equipment of the cellular type, are characterized by the division of the network covering geographic area into a plurality of cells, each one of which is defined as the set of elementary territory areas (pixels) served by the radio-electric signal radiated by the antenna of a fixed radio base station.
Telecommunication networks for third-generation UMTS (Universal Mobile Telecommunications System) radio-mobile terminals use, as known, a radio interface based on the CDMA (Code Division Multiple Access) technique.
Among the known cellular networks, those that use a CDMA access technique show the peculiarity that the same frequency band (channel) can be used in different cells, so that the passage of a mobile terminal from one cell to another neighbor cell (handover) can be managed by using the same frequency. Such technique are called “soft handover”.
The “soft handover” mechanism provides that, in particular areas, called soft handover or macro-diversity areas, a mobile terminal is able to decode the signals from many antennas, and therefore to exchange information with many Radio Base Stations (RBS).
The location of macro-diversity areas and their dimensioning are highly important for the correct operation and cell equipment dimensioning in a telecommunications network since, as obvious, a mobile terminal in macro-diversity engages resources from all Radio Base Stations with which it is simultaneously connected.
A further peculiarity of UTMS networks consists in that such networks are adapted to provide a plurality of services, such as for example:                Telephone;        Fax;        Video-telephone;        Internet access,and that each one of such services generally has service-specific characteristics in terms of speed (number of bits per second) and traffic (amount, symmetrical or asymmetrical).        
It follows that, when planning a network, cell sizing must jointly take into account the characteristics of each service and the possible grouping of services on a single radio carrier, as provided in agreement with the CDMA access technique.
Therefore, planning of UMTS networks, due to its peculiarity, is a complex activity that requires substantially different approaches from those so far used for known mobile networks such as GSM (Global System for Mobile Communication) or IS95 (Interim Standard).
The known methods for simulating UMTS networks can be grouped, according to their approach, into two different families: “statistic” methods and “deterministic” methods.
Statistic methods are mainly based on a Montecarlo type approach (refer to 3GPP TR 25.942 v6.0.0 2002-12—“RF System Scenarios—Release 6”).
The term “Montecarlo simulation” is usually employed for pointing out a static simulation composed of a series of statistically independent “snapshots”. After having fixed the scenario object of the study, each snapshot consists in a realization of a stochastic process generated starting from different distributions of users in the examined area, that simulates the behavior of the examined network. At the end of every snapshot network performance indicators are provided as results. The simulation ends with the statistical analysis of various performance indicators provided by the snapshots, for which their number must be enough to guarantee statistic stability of results that will determine such planning.
It is a rather specific methodology that is particularly adapted to examine performances of a network, for example of the UTMS type, that is scarcely geographically extended, but that, due to an intrinsic model “slowness” due to the statistic convergence of results, cannot be extended to the treatment of networks of such type related to geographic areas that can be compared with those of a nation such as Italy, for example.
Deterministic methods, though keeping the static analysis characteristic, systematically take into account all territory pixels on which the network insists, and clearly are more adapted for planning networks, for example of the UTMS type, related to very wide geographic areas, even if the result generally has smaller levels of compliance with the evolving reality. Different from Montecarlo methods, they have as input a single distribution of users and are carried out in a single simulation without the need of statistic aggregations of results.
Depending on a series of simulations using one of the previously mentioned methods, it is possible to realize a planning process that results in a set of network configuration parameters to be adopted to reach performances that the network must guarantee for the provided users.
Among the objectives in terms of performances of a planning process performed using any simulation method, being a statistic or deterministic one, the “pilot pollution” phenomenon limitation becomes important.
Like every cellular radio-mobile system, the UTMS system too provides for common control channels that are spread within the whole area of each cell. Such channels transmit system information that are mandatory for receiving terminals.
Among these, the CPICH (Common PIlot CHannel) pilot channel is a physical channel in downlink that transmits a predefined sequence of bits at 30 kbit/s and is used by mobile terminals for synchronizing to the network. The pilot channel signal acts as “beacon” to point out the existence of a nearby base station to network receiving terminals.
Each cell transmits its own pilot signal at a common frequency, and with a power that is a fraction of the maximum power that can be radiated by the cell. The comparison between signal powers of different pilot channels allows the terminals to recognize the server base station and to manage possible hand-over processes.
If a terminal is in an area in which it receives the pilot signals of a greater number of cells than the number of cells that can be managed by the terminal and with comparable powers, there results an interference phenomenon known as “pilot pollution” that can create a decreased transmission capability in the area or even the loss of current calls. This phenomenon also implies higher consumption of internal terminal power due to the increase of processing needs. In fact, in such situation, the mobile terminal continuously changes the set of cells to which it is connected in macro-diversity (so-called “active set”), since the number of candidate cells to macro-diversity is greater than the maximum number of cells that can be managed by the terminal itself.
The pilot pollution therefore is an indicator of how many cells in excess are perceived by a radio-mobile terminal when it is connected to a network (and therefore of how many cells in excess would be perceived by a radio-mobile terminal once connected to the network being planned) with respect to its capability of managing cells (maximum number of cells to which it can be connected in macro-diversity) and with respect to parameters being set in the network.
For such purposes, systems and methods are known in the art for planning UMTS networks that take into account the pilot pollution phenomenon, for example the 3g Tool by Aircom International based on a Montecarlo method, and the NPSW (Network Planning. Strategies for WCDMA) Tool by Nokia (see manual: “Radio Network Planning Optimization for UMTS”, Joana et al., Wiley&Sons, 2002) based on a deterministic method.
The Applicant has detected that, from part of the known art, the pilot pollution evaluation is performed based on information related to electromagnetic coverages and parameters set in the network, such as, for example, the macro-diversity depth (in dBm) and the maximum number of cells to which the terminal can be connected in macro-diversity (“active set”). The Applicant has further observed that planning of a network configuration that limits the pilot pollution phenomenon based only on the knowledge of the electromagnetic coverages of the cells does not optimize the use of network resources, since network resources are paid also in areas where they would not be necessary, namely in non-critical areas as regards the service offer profile, where the number of users that access the network is rather small.